The major efferent tracts of the cochlear nucleus (the ventral, intermediate and dorsal acoustic stria) impose a three-way subdivision on the central auditory system as it ascends through the hindbrain. A good deal is already known about the functional role of the ventral system: it is necessary for the discrimination of most of the usual dimensions of normal hearing; that is, for normal thresholds for noises and tones, for discriminating frequency and amplitude of tones, for detecting sounds in noisy environments and for determining the azimuth of a sound source. However, the role of the dorsal system (i.e., dorsal cochlea nucleus or DCN and dorsal acoustic stria or DAS) is unknown. Despite a vast collection of cellular- and molecular-level knowledge about DCN itself, little or nothing is yet known about its contribution to hearing for the deficits in hearing that might accompany its damage as a result of injury or disease. This proposal includes a series of tissue-level ablation-behavior experiments directed at the functional anatomy of the dorsal acoustic system--beginning at DCN's output over the DAS. Animals with and without section of the dorsal (and intermediate) acoustic stria along with appropriate control cases will be tested on two discriminations of sound-source elevation--tasks derived specifically from the only function of the dorsal system yet discovered.